Electrolytes



IN V EN TOR.

SIDNEY D. ROSS HIS ATTORNEY BY/M DMU S. D. ROSS ELECTROLYTES April 26, 1960 Filed June 1l, 1956 FIGI FIGB

' that serves States Patent O 2,934,631 n ELEcTRonYTEs Sidney D. Ross, Williamstown, Mass., assigner to Sprague Electric Company, North Adams, Mass., a corporation of Massachusetts f Application June 1.1, 1956, Serial No. 590,711 Claims. (Cl. 317-230) The present invention relates to a new and improved type of electrolytes. More particularly, it relates to electrolytes which are particularly advantageous for use in various electrical devices, suchv as for example, electrolytic capacitors.

If any author should write a history of the development of electrolytic capacitors, such a volume would be concerned largely with the electrolytes used in such units. Originally, many inorganic aqueous solutions, such as solutions ofvarious inorganic salts, acids or bases, were employed as the electrolytes in such capacitors. Electrolytes of this broad category had many inherent disadvantages, not the least of which is the fact that they could not be employed over a very wide range of temperatures due to the inherent properties of the solvent in such systems. Gradually, through the years the capacitor industry has more or less standardized on electrolytes for electrolytic capacitors which consist of viscous mixtures of polyhydric, glycols, water, and either boric acid or various salts,'such`as ammonium pentaborate. This last category of`electrolytes are comparatively cheap to manufacture and possess comparatively good electrical characteristics. Unfortunately, however, they cannot be used over extremely wide temperature ranges.

It is anfobject of the present invention to produce a new type of electrolyte which can be used over extremely Wide temperature ranges and which possesses comparatively good electrical characteristics. Further objects of theV invention, as well as the advantages of it, will be apparent from the specilication and the appended drawings in` which Fig. l is a front elevation, in section, of a rolldfoil electrode electrolytic capacitor sealed within a can; Figs. Z and 3 are perspective views of the condenser unitofFig. 1 removed frorn the can and partially unrolled to ,show its construction with the former of the polarized type and the latter of the non-polarized type; and Fig. 4 is a'front elevation, in section, of an electrolytic capacitor: having a wire anode.

Briefly, the above aims are achieved by utilizing as a solvent in electrolytic systems organic esters of inorganic acids, such as for example, phosphoric acid, phosphorous acid, phosphonic acid, phosphinous acid, sultinic acid, sulfoni'c acid, sulfuric acid, and vanadic acid.

Thel organic radicals employed with the invention in forming organic esters are preferably alkyl in nature. Highlyf suitable alkyl radicals are methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, amyl, etc. Preferably, such alkyl radicals are selected from the groupof lower alkyls containing no more than six carbon atoms. Suitable. aryl` esters may also be employed as solvents within the broad scope of the instant invention.

Thesey solvents taught herein are used with a salt of a non-metallic cation and an oxidizing anion as both formation and working electrolytes in electrolytic capacitors having at as the dielectric. The electrode can be of any one of the common hlm-forming valve metals particularly least one electrode coated with an oxide layer i '2,934,681 Patented Apr. 26, 1960 'ice a sufficiently high dielectric constant, which features are Y highly desirable for use in electrical applications. Thus, ythese esters listed hereafter are highly desirable for use in electrical applications. Thus, these esters listed hereafter are highly suitable as solvents in the broad scope of the instant invention and indicative of the specific solvents falling within the preferred classes:

I. TERTIARY PHOSPHATE ESTERS a. Compounds with the ester linkage to an aliphatic carbon Boiling points (1) Hydrocarbon derivatives- C./ mm. pressure) Trimethyl phosphate 197.2/760 Dimethyl thiomethyl phosphate, (CH3O)2(CH3S)PO 107/20 Dimethyl ethyl phosphate 203.3/ 760 Triethyl phosphate 216/770 Ethyl thiophosphate 216/ 745 Trithioethyl thiophosphate, (C2H5S)3PS 182/ 20 Tripropyl phosphate 138/ 47 Tri-n-butyl phosphate 180/20 Diethyl butyl phosphate 123/15 Tri-isoa'rnyl phosphate 143/ 3 Butyl di-isoamyl phosphate 4.5 (2) Halogen derivatives- Diethyl, 2 lluoroethyl phosphate,

(C2H5O)2(FCH2CH2O)PO 123/ 13 Diethyl-Z-chloroethyl phosphate 144/ 18 (3) Derivatives with hydroxy group- Dimethyl l-methoxy ethyl phosphate 112/ 9 Tri-l-ethoxy ethyl phosphate 225 20 (4) Carboxylic derivatives Diethyl[l-methyl2(ethyl carboxylate)] vinyl phosphate, (C2H5O)2(C2H2OCCH=CCH3O)PO 138/ 2 Diethyl [l-rnethyl-Z-(ethyl carboxylate)] vinyl thiophosphate, (C2H5O)2(C2H5OCCH=CCH3O)PS 154/5 b. Compounds with ester linkage zo a cyclic structure (l) Derivatives of cyclic hydrocarbons- Diethylphenyl phosphate 200/ 70 Dibutylphenyl phosphate 183/ 15 Naphthyl di-isoamyl phosphate 142/().5 (2) Halogen derivatives-diethyl 2 chlorophenyl phosphate 140/2 Il. TRIALKYL VPHOSPHITES yTriethyl phosphite /757 Tripropyl phosphite 206/ 760 Y Tributylphosphite 127/ 18 Tri-isobutyl phosphite 13S/l0 Triisoamyl phosphite 207/760 earnest4 Boiling points C./mm. pressure) Dnethyl methane phosphonate 18,1/ 760 Diethyl methane phosphonate Y 192/ 760 Di-n-tolyl methane phosphonate 200/7v Diethyl ethane phosphonate 203/ 750*V Dibutyl ethane phosphonate 137/17 IV. NEUTRAL ESTERS OF PHOSPHINOS ACIDS Ethyl-Z-bromo ethyl-ethylphosphinate 129/11Y Ethyl-ethylphenylphosphinate 162/ l6 Dipropyl ethyl phosphinate 103/15v Methyl phenyl ethyl phosphinate 12'5/15 Ethyl phenyl ethyl phosphinate 137/15 Bis(phenyl) phenyl phosphinate` 2651/62" Dibutyl ethyl phosphinate 116/ l5- It must be realized that the broad concept of this inven-V tion is directed toward the use of. non-aqueous solvents for electrolytic solutes lytic solution having a tion in addition to the are utilized in the electrical industry, and in particular, where these electrolytes are used in electrolytic capacitors, they must oier systems which are stable under high electrical stress, must allow dissociation of the solute so that the solution offers low resistive ionic conduction, and must facilitate the film formation on the part of the solutes of the valve metal which is used as` at least oneof the electrodes. In addition to these phosphorous containing compounds which have been set forth as a preferred group, there are many organic esters of. inorganic acids falling within the scope of this present invention which meet the requirements imposed by they use of electrical components. The broad classes of these Ycompounds which additionally fulfill these requirements, are the organic esters, preferably alkyl esters, of the followinggeneral classes of inorganic acids: sulnic acid,` sulfonicacid, sulfuric acid, and vanadic acid.

The following specific compounds are indicative of those having the chemical, physical and electrical properties so as to come Within the broad scope of this invention:

Sulnc acid-Ethyl ethanesullinate', butyl ethanesuliinate, butyl butanesuliinate.

Sulfurc acid-Ethylene sulfate and trimethylene sulfate, ethyl-n-propyl sulfate, ethyl-n-butyl sulfate.

Sulfonic acid.-Methylptoluene sulfonate, ethyl-p-toluene sulfonate, and 5,2(CH3)2CH(CH3)C6H3 benzene sulfonate.

Vanadic acd.-Triethyl vanadate, tri-isopropyl vanadate.

Certain organic esters of inorganic acids alternatively are unsuitable for use with this invention because they do not possess the broad range of liquidity and/or the stability under electrical stress and elevated temperatures necessary. Such a class of esters are the boric acid esters which appear to readily deteriorate upon operation in an electrolytic capacitor.

The solutes which are useful in the non-'aqueous electrolyte systems are salts of a non-metallic cation and a film-forming anion. By the term film-forming anion? is meant an ion readily reducible at the anode so as'to effect reparation of the oxide film should any injury of the film occur during operation, or if used in the formation process, to produce the desired dielectric lm. The nonmetallic cations thus include ammonium and organic substituted ammonium radicals such as tri-n-butylammonium, tri-ethanolammonium, urea, diethanolammonium, etc. The film-forming anion on the other hand includes the acetate ion, arsenate ion, borate ion, phos` phate ion, picramate ion, tartrate, vanadate, chromate,

dichromate, permanganate, nitrate, molybdate, formate, etc.v Thus salts illustrative of this invention include am# monium acetate, ammonium arsenate, ammonium nitrate,

which makes 'possible'an electro-Y wide temperature rangeA of opera requisites for electrolytes'. whichamonium oxalate, and the reaction product of a compound under the A list with a copound under the B list below:

A Organic amines Organic hydroxyl amines Organic hydrazi'nes Quinazerin-Z-sulfonic acid Flavianic Acid Anthraquinone 2,6-disulfonic acid 2,4,6-trinitrophenyl acetic acid Alizirin sapherole B Picric acid 2,4,6-trinitroresorcinol styphnic acid 3,5-dinitro-o-creso1 2,4-dinitro phenol 2,4-dinitro phenyl acetic acid 2,4,6-trinitrophenoxy acetic acid Anthraquinone-Z-sulfonic acid 2,5-dihydroxy quinone Tetrahydroxy quinone In the utilization of the various solutesset forth in this specification, consideration must be Ygiven to two funda` mental aspects, namely the level of solubility required .for any desired application and the ability of the oxidizing" portion of the solute to perform its fundamentaltask'in' the solvent which is being used.

Preferably, the solutes used form 1/2 to about '20% Smaller amounts of solute, however,

form of capacitors shown in Figs. l, 2'and- 3, the con` denser unit 1 is of the rolled foil'type being made'up ofaA pair of foils 2, 3 formed of a film-forming metal`s'l'1`ch'as tantalum, aluminum and zirconium spaced from one an other by layers 4 and 5 of a condenser paper, such as calendered or uncalendered kraft paper. In 1"ig.-2y whichl is directed to the polarized electrolytic construction, the anode 3 has an oxide hn 6 on a surface, while the cathode foil 4 does not have an appreciable dielectric'oxide coat# ing. The non-polarized uniti of Fig. v3 foralterna'ting:

current applications has an oxide dielectric lm 6 on both of the electrode foils 3 and 4. The assembly of'lfoil and kraft paper is rolled into a compact cylinder. Metal terminals 8 and 9, preferably formed of by spot welding or crimping.

The condenser unit 1,

copper. The terminals 8 and 9 extend fromthe respective ends of the tubular can 11,

section. Positioned against the inner surface of the tubular can 11 is a tube of kraft paper 13fwhich -is satu rated with the electrolyte 14.

In the form of the condensershown in Fig. 4,7"the'a1i` ode is in the form 'of an oxide coated etched or `unetch`ed wire of the film-forming metals previously set'forth. The

total capacity required. The tubular can 22 of a metal such as silver.

24 and a paper spacer disc 25 cooperatingthe spacer disc 25 and its other end ylled! circling resin gasket 30 The paper tube a millimeter or plastic seal 26.

a ratio of from`ab'out` by weight'of the solvent present'.

can be used quite" advantageously in certain limited applications. VIn the the same metal; as the foils, are fastened to the ends ofthe respective foils as' impregnated with the electrolyte of the invention, is enclosed in a tubular can 11 of a suit- -V able non-corrosive metal such as silver or silver platedV passing through a resinous Y end seal 12 which confines the electrolyte to the'wound that can be pushed into/thecan.-v 24 is short enough to permitzthe 'gasket`- 30 to be forced into the can and leave abovefit`at=leastvvvr so of height' toreceive andv anchora- Priorto placing. the anode -wire==28 gassosi 34 is placed in the container and the outer end of the anode wire 28 attened as shown at 36. Also, before insertion of the anode wire 28, a ilexible lead wire 38 of nickel for example can have its end welded to the flattened portion 36, preferably by a spot weld. To the outside of the blind end of the can 22, there is fastened by solder 40 another lead wire 42.

A number of typical examples of the practice of my invention are given below. Electrolytic capacitors were made up consisting of 41/2 mil thick aluminum foils of 99.99% purity etched and formed in boric acid solution to 375 v. of 1square inch area as the anodes, l mil unformed unetched aluminum foils as the cathodes, and 4 mil glass paper separators between the anode and cathode.

An electrolyte consisting of 1 gram tri-nbutyl ammonium picrate (recrystallized from alcohol) dissolved in 50 cc. of tri-n-butyl phosphate (the solvent was redistilled from the commercially available product obtained from the Commercial Solvents Corporation, at a boiling point of 142 C. at a pressure of 0.25 mm.) was introduced into the aforementioned capacitor structure at room temperature. The unit was found to have a temperature operational range in excess of from 60 lC. to |200o C. and was characterized by a very low internal resistance, yunusually constant capacitance over the entire temperature range, and was further featured by a relatively stable low dissipation factor over this range. The capacitance varied from about 1 microfarad per square inch of anode surface area at 60 C. to about 1.3 microfarads per` square inch of anode surface area at l-200" C.

Similar results are also obtained with the following electrolytes phosphate 6% of ammonium acetate and 94% of tri-isobutyl phosphite 6% tri-n-propyl ammonium picrate and 94% of diethyl ethane phosphonate 5% tri-n-propyl ammonium picrate and 95% dipropyl ethyl phosphinate 15% triethanol ammonium picrate and 85% ethyl phenyl ethyl phosphinate As shown above, this invention constitutes a decided improvement over previously known electrolytic systems in that the use of the disclosed solvents and in particular the preferred phosphorous compounds as solvents in 200 C. and higher. Additionally, these systems are not corrosive in nature and are further characterized by such low vapor pressures at elevated temperatures that in most applications venting of the electrolytic capacitor or electrical component is not necessary. A preferred class of organo phosphorous compounds are stable neutral esters which are non-toxic in nature, electrically stable to high electrical stress and are susceptible to simple impregnation techniques.

An electrical device which is operable over the extreme temperature range which has been indicated in this specication of necessity undergoes marked physical structural changes when traversing the entire breadth of this range. Many applications find the construction of Fig. 1 suitable, although in high temperature units, the containment of my liquid electrolytes may present possible diiculties unless suitable measures are taken to prevent their egress. In addition to preventing egress of the electrolyte from the containing structure of the electrical device, it is necessary to maintain the electrodes fully insulated, one from the other, and for thisk reason, the plastic dielectrics are finding rapid acceptance as dielectric gaskets and washers of high resistivity and inertness chemically. It has been found practical to contain the electrolyte within the electrical component for high temperature applications by utilizing a structure similar to that forming the basis of a U.S. patent application by Walter S. Schroeder, Serial No. 340,710, tiled March 6, 1953, and now abandoned, which has been modified by the insertion of a steel spring washer at the bottom of the cup-like or alternatively a tube-like container. The crimping assembly is such that the capacitor structure is forced downwardly against the steel spring washer so that it remains in a continual stressed state which thus serves to yield su'icient pressure over the entire temperature range so as to prevent egress of the liquid electrolyte from the electrical device.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof except as defined in the appended claims.

This application forms a continuation-impart of my copending United States patent application, Serial No. 365,519, tiled July 1, 1953, and now abandoned.

I claim:

1. An electrolytic capacitor having a plurality of electrodes, one of said electrodes being a formed valve metal, and a non-aqueous electrolyte contiguous with said electrodes comprising a solute of the salt of a non-metallic cation and an oxidizing anion dissolved in a stable organic ester acid of the group consisting of phosphoric, phosphorous, phosphinous and phosphonic acids.

2. The capacitor of claim 1 in which the solvent is a trialkyl phosphite.

3. The capacitor of claim 1 in which the solvent is a completely esterilied phosphoric acid.

4. The capacitor of claim 1 in which the solvent is a completely esteried phosphonic acid.

5. The capacitor of claim 1 in which the solvent is a completely esteriiied phosphinous acid.

6. A non-aqueous electrolytic system for capacitor electrolytes consisting essentially of a solute of a salt of a non-metallic cation and an oxidizing anion dissolved in a stable organic ester of acid of the group consisting of phtsphoric, phosphorous, phosphinous and phosphonic aci s.

7. A system as claimed in claim 6 in which the solvent is a trialkyl phosphite.

8. A system as claimed in claim 6 in which the solvent is a completely esteritied phosphoric acid.

9. A system as claimed in claim 6 in which the solvent is a completely esteriiied phosphonic acid.

10. A system as claimed in claim 6 in which the sol vent is a completely esterified phosphinous acid.

References Cited in the le of this patent UNITED STATES PATENTS 1,959,130 Hambuechen May 15, 1934 2,321,997 Compton June 15, 1943 2,566,908 Ruscetta Sept. 4, 1951 2,759,132 Ross Aug. 14, 1956 2,786,165 Ross Mar. 19, 1957 2,830,237 Ross Apr. 8, 1958 

1. AN ELECTROLYTIC CAPACITOR HAVING A PLURALITY OF ELECTRODES, ONE OF SAID ELECTRODES BEING A FORMED VALVE METAL, AND A NON-AQUEOUS ELECTROLYTE CONTIGUOUS WIT SAID ELECTRODES COMPRISING A SOLUTE OF THE SALT OF A NON-METALLIC CATION AND AN OXIDIZING ANION DISSOLVED IN A STABLE ORGANIC ESTER ACID OF THE GROUP CONSISTING OF PHOSPHORIC, PHOSPHOROUS, PHOSPHINOUS AND PHOSPHONIC ACIDS. 